Preoperative breast MRI detected additional, otherwise undetectable malignancies in either the ipsilateral or the contralateral breast in 1 of 10 subjects in a study of 155 women with newly diagnosed breast cancer.

Still, the imaging procedure also carried a “considerable” 80% false-positive rate, heightening patient anxiety and leading to further diagnostic work-ups that ultimately proved to be unnecessary, wrote Dr. Bilimoria and his associates at Northwestern University, Chicago.

Of even more concern was the fact that the MRI results prompted more extensive surgery than originally planned in several cases in which it was later found that the less extensive surgery would have sufficed. These included two ipsilateral mastectomies and three contralateral prophylactic mastectomies that later proved to have been unnecessary.

To determine how routine breast MRI would affect surgical management of newly diagnosed breast cancer, the researchers reviewed data from 155 women aged 34–75 years who were diagnosed and treated by a single surgeon in 2005–2006. All had undergone “exhaustive” evaluation by mammography and ultrasonography, then biopsy of the suspicious lesion, after which a surgical plan had been developed (Arch. Surg. 2007;142:441–7).

At that juncture, bilateral breast MRI was performed. If any additional lesions were detected, the patient had second-look ultrasonography or mammography, followed in some cases by biopsy of the MRI-detected lesion. The original surgical plan could then be altered according to the results of these exams.

Overall, breast MRI changed the surgical plan in 36 (23%) of the study subjects. Ten women who initially were scheduled for breast-conserving therapy were “upgraded” to mastectomy, and 21 required a wider excision but still were able to have a lumpectomy. The remaining five had an MRI-detected lesion in the contralateral breast and underwent prophylactic mastectomy.

Pathologic findings showed that switching to more extensive surgery was appropriate because suspicious lesions proved to be malignant in 8 of the 10 who upgraded to mastectomy, 5 of the 21 who upgraded to wider excision, and 2 of the 5 who had prophylactic mastectomy of the contralateral breast. Thus, the change in surgical plan was deemed “beneficial” in 42% of the women who had such a change, which was approximately 10% of the entire study population, Dr. Bilimoria and his associates said.

“Therefore, 10 women must undergo a breast MRI for 1 to have a beneficial change in management,” they said.

The overall false-positive rate in this study was 80%, because 58 of the 73 MRI-detected suspicious lesions proved to be benign.

The researchers acknowledged that some experts would consider many of the malignant MRI-detected lesions to be clinically irrelevant. “However, if we believe that it is important to clear lumpectomy margins of microscopic disease to minimize the risk of local recurrence, it would follow that small foci detected on MRI also warrant identification and excision,” they said.

In a written discussion accompanying this report, Dr. Baiba J. Grube of Yale University, New Haven, Conn., said that although the authors deemed changes in the surgery plan to be “beneficial” if suspicious lesions proved to be malignant, clinicians should do so only if the surgical “upgrades” improved patient survival or quality of life—two factors that were not addressed in this study (Arch. Surg. 2007;142:445–6).